The term oil sands generally refers to a mixture of sand, clay and other minerals, water, and bitumen. Oil sands bitumen is very dense and highly viscous (i.e., resistant to flow). At room temperature, oil sands bitumen has the consistency of cold molasses, which makes it difficult to transport.
Resource estimates indicate that oil sands deposits are located throughout the world in varying amounts. By far, the two largest estimated deposits of oil sands are in Canada, particularly the Province of Alberta, and in Venezuela's Orinoco Oil Belt. It has been estimated that Canada has as much as 1.7 trillion barrels of “discovered” oil sands bitumen.
Perhaps a more useful estimate of oil resources is “proven reserves.” According to the Energy Information Administration (EIA), proven energy reserves are “estimated quantities of energy sources that analysis of geologic and engineering data demonstrates with reasonable certainty are recoverable under existing economic and operating conditions.” See EIA Glossary at http://www.eia.gov/. The Government of Alberta estimates that its proven oil sands reserves are approximately 170 billion barrels, which accounts for 97% of Canada's total proven oil reserves, 7%-10% of the total estimated resource in Canada's geologic basin. See, Oil Sands and the Keystone XL Pipeline: Background and Selected Environmental Issues, Congressional Research Report for Congress, Jonathan L. Ramseur, Coordinator, Feb. 21, 2013.
Estimates of U.S. oil sands deposits vary. According to a “measured-in-place” estimate from the U.S. Geological Survey (USGS), deposits of oil sands in the United States may contain approximately 36 billion barrels. The estimated resource of U.S. oil sands is located in several states in varying amounts: Alaska (41%), Utah (33%), Texas (11%), Alabama (5%), California (5%), and Kentucky (5%).
The deposits are not uniform. For instance, some deposits (estimated at less than 15%) in Utah may be amenable to surface mining techniques. In contrast, the Alaska deposits are buried below several thousand feet of permafrost.
Bitumen (i.e., natural bitumen from oil sands) differs fundamentally from other petroleum oils such as heavy oil, medium oil, and conventional (light) oil. Differences in petroleum oils occur over time, as lighter fractions of the petroleum oils can be lost through natural processes. The result is that petroleum oils become heavy, with a change in chemical composition. In general, as conventional light oil degrades from medium oil to heavy oil to bitumen through natural processes, increases may be seen in density (shown as reductions in API gravity), coke, asphalt, asphaltenes, asphaltenes+resins, residuum yield (percent volume), pour point, dynamic viscosity, and the content of copper, iron, nickel, vanadium among the metals and in nitrogen and sulfur among the non-metals. For example, a heavy oil may exhibit an API gravity of 15-17 degrees, an asphaltene content of 11-13 wt %, and a Conradson Carbon content of 7-9 wt %; whereas a bitumen oil may exhibit an API gravity of 5-7 degrees, an asphaltene content of 25-27 wt %, and a Conradson Carbon content of 12-14 wt %.
Currently about 1.5 million barrels of bitumen oil per day are extracted from Canadian oil sands. A substantial portion of the extracted Canadian bitumen is transported to the United States, where it is upgraded into fuel products.
The majority of the bitumen oil that is upgraded into fuel products is produced through a combination of strip mining and a water-based extraction process. Large quantities of water (2-4 barrels per barrel of oil) are required to obtain a single barrel of oil from the oil sands.
Oil sands companies are currently held to a zero-discharge policy by the Alberta Environmental Protection and Enhancement Act (1993). Thus, all oil sands process water produced must be held on site. This requirement has resulted in over a billion cubic meters of tailings water held in containment systems. Those that produce the tailings water have been held responsible for reclaiming the water and finding a way to release the reclaimed water back into the local environment.
Despite extensive programs that have led to significant improvements including up to 90+% use of recycled water, the tailings ponds and buildup of contaminants in the recycled water and in tailings ponds represent what is considered to be a fundamentally non-sustainable process.
Waterless approaches using hydrocarbon solvent extraction technology have been examined. These approaches offer a pathway to obtaining oil from oil sands that could be potentially low energy, water free, and environmentally superior to the current water-based technology.
U.S. Pat. No. 3,475,318 to Gable et al. is directed to a method of selectively removing oil from oil sands by solvent extraction with subsequent solvent recovery. The extraction solvent consists of a saturated hydrocarbon of from 5 to 9 carbon atoms per molecule. Volatile saturated solvents such as heptane, hexane and non-aromatic gasoline are used to selectively remove saturated and aromatic components of the bitumen from the oil sand, while leaving the asphaltenes on the sand. In order to remove the asphaltenes for process fuel, an aromatic such as benzene or toluene is added to the solvent at a concentration of from 2 to 20 weight percent.
U.S. Pat. No. 4,347,118 to Funk et al. is directed to a solvent extraction process for tar sands, which uses a low boiling solvent having a normal boiling point of from 20° C. to 70° C. to extract the bitumen from the tar sands. The solvent is mixed with tar sands in a dissolution zone at a solvent:bitumen weight ratio of from about 0.5:1 to 2:1. This mixture is passed to a separation zone containing a classifier and countercurrent extraction column, which are used to separate bitumen and inorganic fines from extracted sand. The extracted sand is introduced into a first fluid-bed drying zone fluidized by heated solvent vapors, to remove unbound solvent from extracted sand and lower the water content of the sand to less than about 2 wt. %. The treated sand is then passed into a second fluid-bed drying zone fluidized by a heated inert gas to remove bound solvent. Recovered solvent is recycled to the dissolution zone.
U.S. Pat. No. 7,985,333 to Duyvesteyn is directed to a method for obtaining bitumen from tar sands. The method includes using multiple solvent extraction or leaching steps to separate the bitumen from the tar sands. A light aromatic solvent such as toluene, xylene, kerosene, diesel (including biodiesel), gas oil, light distillate, commercially available aromatic solvents such as Solvesso 100, 150, and 200, naphtha, benzene and aromatic alcohols can be used as a first solvent. A second hydrocarbon solvent, which includes aliphatic compounds having 3 to 9 carbon atoms and liquefied petroleum gas, can also be used in a second extraction process.
U.S. Patent Pub. No. 2009/0294332 to Ryu discloses an oil extraction process that uses an extraction chamber and a hydrocarbon solvent rather than water to extract the oil from oil sand. The solvent is sprayed or otherwise injected onto the oil-bearing product, to leach oil out of the solid product resulting in a composition comprising a mixture of oil and solvent, which is conveyed to an oil-solvent separation chamber.
U. S. Patent Pub. No. 2010/0130386 to Chakrabarty discloses the use of a solvent for bitumen extraction. The solvent includes (a) a polar component, the polar component being a compound comprising a non-terminal carbonyl group; and (b) a non-polar component, the non-polar component being a substantially aliphatic substantially non-halogenated alkane. The solvent has a Hansen hydrogen bonding parameter of 0.3 to 1.7 and/or a volume ratio of (a):(b) in the range of 10:90 to 50:50.
U. S. Patent Pub. No. 2011/0094961 to Phillips discloses a process for separating a solute from a solute-bearing material. The solute can be bitumen and the solute-bearing material can be oil sand. A substantial amount of the bitumen can be extracted from the oil sand by contacting particles of the oil sand with globules of a hydrocarbon extraction solvent. The hydrocarbon extraction solvent is a C1-C5 hydrocarbon.
U. S. Patent Pub. No. 2012/0261313 to Diefenthal et al. is directed to a process for producing a deasphalted bitumen composition from oil sand that uses a solvent comprised of a hydrocarbon mixture. The solvent is injected into a vessel and the oil sand is supplied to the vessel such that the solvent and oil sand contact one another in the vessel, i.e., contact zone of the vessel. The process is carried out such that not greater than 80 wt % of the bitumen is removed from the supplied oil sand, with the removal being controlled by the Hansen solubility blend parameters of the solvent and the vapor condition of the solvent in the contact zone. The extracted oil and at least a portion of the solvent are removed from the vessel for further processing as may be desired.
U.S. Patent Pub. No. 2013/0220890 to Ploemen et al. is directed to a method for extracting bitumen from an oil sand stream. The oil sand stream is contacted with a liquid comprising a solvent to obtain a solvent-diluted oil sand slurry. The solvent-diluted oil sand slurry is separated to obtain a solids-depleted stream and a solids-enriched stream. The solvent-to-bitumen weight ratio (S/B) of the solids-enriched stream is increased to produce a solids-enriched stream having an increased S/B weight ratio and a liquid stream. The solids-enriched stream having an increased S/B weight ratio is filtered to obtain the bitumen-depleted sand. The solvent can include aromatic hydrocarbon solvents and saturated or unsaturated aliphatic hydrocarbon solvents.
There is a continuing need for waterless approaches using hydrocarbon solvent extraction technology to extract the bitumen material from oil sand. There is also a need for converting the extracted bitumen to transportation fuels in a manner that produces greater quantities of the fuels, reduces overall hydrogen consumption, and reduces overall negative environmental impact compared to current processes.